Examination device

ABSTRACT

The present invention provides an inspection device that is capable of detecting foreign matter with high accuracy, the inspection device including: a light source; an electro-optic element on which light from the light source is incident and which changes a phase of the light into at least two states; and a controller. The controller corrects a phase fluctuation of the electro-optic element itself, using intensity modulation characteristics of the eletro-optic element which are obtained by changing an applied voltage that is input to the electro-optic element.

TECHNICAL FIELD

The present invention relates to an inspection device that inspectsminute foreign matter.

BACKGROUND ART

As the background art of the technical field, JP-T-2009-501902 (PTL 1)describes that “there are provided an inspection system, a circuit, anda method for enhancing flaw detection by taking measures of saturatedlevels of an amplifier and an analog/digital circuit as a limitingfactor of a measurement detection range of an inspection system, andthere are provided an inspection system, a circuit, and a method forenhancing flaw detection by reducing thermal damage to large particlesdue to a dynamic change in an incident laser/beam power/level at whichincident laser beams are supplied to a specimen during scanning ofsurface inspection taking measures of saturated levels of an amplifierand an analog/digital circuit as a limiting factor of a measurementdetection range of an inspection system” (see Abstract).

In addition, as described in JP-A-2001-144357 (PTL 2), means forswitching and applying a predetermined voltage with respect to a Pockelscell is provided as means for driving the Pockels cell.

Further, a foreign matter inspection device for a semiconductor waferdetects a minute flaw that is present on a wafer surface, and outputsthe number, a coordinate, or a size of the flaw. Due to theminiaturization of a semiconductor process, there is a demand forimprovement of detection sensitivity in the foreign matter inspectiondevice. There is a method for achieving high intensity of illuminationlight as an example of means for improving the detection sensitivity.However, when irradiation is performed with the illumination lighthaving high intensity, large foreign matter having a size that exceedshundreds of nm is broken. In this specification, this phenomenon isreferred to as explosive fracture. Since fragments from the explosivefracture are spread over a specimen surface and a flawed region of thespecimen is increased, an inspection power (intensity of illuminationlight used for inspection) needs to be limited.

In the specification of U.S. Pat. No. 7,787,114 (PTL 3), a technology ofdynamically controlling an inspection power during inspection usingPockels cells is disclosed. In PTL 1, normally, while inspection isperformed with high sensitivity by high-power irradiation, theinspection power is reduced during the inspection on foreign matter andthe vicinity thereof such that explosive fracture is avoided in a casewhere there is large foreign matter.

CITATION LIST Patent Literature

PTL 1: JP-T-2009-501902

PTL 2: JP-A-2001-144357

PTL 3: U.S. Pat. No. 7,787,114

SUMMARY OF INVENTION Technical Problem

In a case where the inspection device for minute foreign matter operatesfor a long time, characteristics of a crystal change due to an influenceof a laser power of a laser beam passing through the Pockels cell. Dueto the characteristic change, there is a possibility that a rotatingangle of a polarization plane of the laser beam passing through thePockels cell will fluctuate and thus the laser power with whichirradiation is performed on a wafer as the specimen will change.Therefore, scattered light intensity from the foreign matter on thewafer changes and thus it is difficult to detect a diameter of theforeign matter with high accuracy. However, there is no consideration ofthe change and detection difficulty in PTLs 1 and 2.

In addition, as PTL 3, in a case where the inspection is performed withhigh sensitivity due to high-power laser beam irradiation, the specimenwill be irradiated with a laser beam having a high power in a case wherethe Pockels cell itself or a Pockels cell control unit is out of orderand then abnormally stops. In the prior art, there is no considerationfor the problems.

Further, since control voltage is likely to change depending on atemperature state of the Pockels cell itself, there is a possibilitythat it is not possible to control the laser power intended to beachieved even when a predetermined voltage is applied. In other words,the voltage characteristics of the Pockels cell itself change, andthereby there is a possibility that the specimen is likely to beirradiated with the laser beam having an excessive power which is notintended to be achieved.

The present invention provides an inspection method and an inspectiondevice that is capable of inspecting foreign matter with high accuracy.

In addition, an object of the present invention is to safely control thelaser power in an apparatus that controls the laser power by using anelectro-optic element such as the Pockels cell.

Solution to Problem

In order to solve such problems described above, configurationsdescribed in claims are adopted.

The present application includes a plurality of types of means thatsolve the problems described above. As an example thereof, an inspectiondevice includes: a light source; an electro-optic element on which lightfrom the light source is incident and which changes a phase of the lightinto at least two states; and a controller. The controller corrects aphase fluctuation of the electro-optic element itself, using intensitymodulation characteristics of the eletro-optic element which areobtained by changing an applied voltage that is input to theelectro-optic element.

Advantageous Effects of Invention

According to the present invention, it is possible to detect minuteforeign matter with high accuracy.

In addition, according to the present invention, even in a case where apower control system is out of order, it is possible to minimize a riskof damaging a specimen.

Problems, configurations, and effects other than the problems,configurations, and effects described above are clarified in thefollowing description of embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a foreign matterinspection device according to a first embodiment.

FIG. 2 is a block diagram showing a configuration of a driver circuitaccording to the first embodiment.

FIG. 3 is a graph showing an operation of the driver circuit accordingto the first embodiment.

FIG. 4 is a block diagram showing a configuration of a driver circuitaccording to a second embodiment.

FIG. 5 is a block diagram showing a configuration of a driver circuitaccording to a third embodiment.

FIG. 6 is an example of a block diagram showing a configuration of aforeign matter inspection device according to a fourth embodiment.

FIG. 7 is a block diagram illustrating an entire configuration of anoptical inspection device according to a fifth embodiment.

FIG. 8 is a block diagram showing a configuration of an illuminationoptic system of the optical inspection device according to the fifthembodiment.

FIG. 9 is a block diagram showing another configuration of a powermonitor system of the illumination optic system of the opticalinspection device according to the fifth embodiment.

FIG. 10 is a graph illustrating a relationship (intensity modulationcharacteristics) between a Pockels cell applied voltage and aninspection power of the optical inspection device according to the fifthembodiment.

FIG. 11 is a graph illustrating an applied voltage to the Pockels cellof the optical inspection device according to the fifth embodiment.

FIG. 12 is a graph illustrating an influence of a temperature on voltagecharacteristics (intensity modulation characteristics) of Pockels cellof the optical inspection device according to the fifth embodiment.

FIG. 13 is a flowchart showing flow of a process for performingoptimization of the voltage characteristics (intensity modulationcharacteristics) and a half-wave plate placement angle of the Pockelscell before inspection is performed by the optical inspection deviceaccording to the fifth embodiment.

FIG. 14 is a table illustrating effects of a half-wave plate in theoptical inspection device according to the fifth embodiment.

DESCRIPTION OF EMBODIMENTS

The present invention relates to an inspection device that irradiates aspecimen surface with a laser beam for a predetermined time and inspectsa flaw on the specimen surface. The inspection device is configured toinclude: a laser beam source that emits a laser beam with which thespecimen surface is irradiated; a modulation unit that modulates theemitted laser beam; a controller that controls a voltage which isapplied to the modulation unit; and a reflected light detecting unitthat detects scattered light reflected from the specimen surface andgenerates a detection signal. The controller performs control to switchthe voltage that is applied to the modulation unit, based on a detectionresult obtained by the reflected light detecting unit.

In addition, an inspection device that inspects a specimen with a laserbeam has an illumination optical system that includes: a laser beamsource that emits a laser beam; an electro-optic element on which thelaser beam from the laser beam source is incident and which changes aphase of the laser beam into at least two states; and a wave plate thatrotates the phase of the laser beam. The wave plate is configured togenerate a phase difference with which intensity of the laser beam, withwhich the specimen is irradiated in a state in which no voltage isapplied to the electro-optic element, is attenuated to be lower than themaximum intensity obtained in a state in which a voltage is applied tothe electro-optic element.

Hereinafter, examples will be described with reference to the figures.

Example 1

In this example, there is provided description of an example of aforeign matter inspection device that switches laser powers with whichirradiation is performed on a wafer during inspection and has a stableirradiation laser power for a long time.

FIG. 1 is an example of a diagram of a configuration of the foreignmatter inspection device of the example.

A foreign matter inspection device 100 includes a laser beam source 2,an optical modulation element 3, a polarization plate 4, a beam splitter5, a mirror 6, lenses 7 and 8, a sensor 9, a detection circuit 10, adata processing unit 11, a driver circuit 12, beam power detecting means13, and a stage 14.

In the foreign matter inspection device 100, a wafer 1 is mounted on thestage 14, and irradiation with a laser beam that is emitted from thelaser beam source 2 is performed on the wafer 1 via the opticalmodulation element 3, the polarization plate 4, the beam splitter 5, themirror 6, and the lens 7. At this time, in the foreign matter inspectiondevice 100, the wafer 1 is subjected to rotational movement by the stage14 and is subjected to linear movement by a translation stage (notillustrated), and thereby the laser beam, with which the irradiation isperformed on the wafer 1, has a spiral trajectory over the entiresurface of the wafer 1. Thus, it is possible to inspect the entiresurface of the wafer 1. In addition, scattered light from foreign matteron the wafer 1 is detected via the lens 8, the sensor 9, and thedetection circuit 10, and the data processing unit 11 performs foreignmatter determination based on detection results from the detectioncircuit 10.

In the foreign matter inspection device 100 according to the example,the driver circuit 12 switches applied voltage to the optical modulationelement 3 through switching control from the data processing unit 11.The presence or absence of foreign matter having a large diameter ispredicted in the data processing unit 11, based on the detection resultsin a previous cycle in which scanning is performed on the wafer in aspiral shape, and the data processing unit controls the voltageswitching by the driver circuit 12. Specifically, in a case where thepresence of the foreign matter having a large diameter is predicted inthe data processing unit 11, a laser power with which irradiation isperformed on the wafer 1 is reduced.

By a predetermined voltage switched by the driver circuit 12, theoptical modulation element 3 controls rotation of a polarization planeof a laser beam passing through the optical modulation element andcontrols the laser power of a laser beam passing through thepolarization plate 4. Specifically, in a case where the presence of theforeign matter having a large diameter is predicted in the dataprocessing unit 11, the driver circuit 12 is to output a predeterminedvoltage by which the laser power with which the irradiation is performedon the wafer 1 is reduced. On the other hand, in a case where theabsence of the foreign matter having a large diameter is predicted, thedriver circuit 12 outputs a predetermined voltage by which the laserpower is increased.

In addition, in the data processing unit 11, the beam power detectingmeans 13 detects the laser power with which the irradiation is performedon the wafer 1 via the beam splitter 5, and a voltage value that isswitched by the driver circuit 12 and is output to the opticalmodulation element 3 is controlled. This is because, although theoptical modulation element 3 applies the same control voltage as thatfrom the driver circuit 12, due to an environmental condition such as atemperature, a rotating angle of the polarization plane of the laserbeam passing through the optical modulation element 3 is different and,as a result, the laser power with which the irradiation is performed onthe wafer 1 fluctuates. Since detection accuracy of the foreign matteron the wafer 1 is degraded when the laser power fluctuates, the voltagethat is switched by the driver circuit 12 is controlled such that theirradiation is performed on the wafer 1 with predetermined laser powervia the beam power detecting means 13. Hence, the detection accuracy ofthe foreign matter is improved.

FIG. 2 is an example of a configuration of the driver circuit 12 in theforeign matter inspection device 100.

The driver circuit 12 is configured to include an input circuit 51,high-voltage generating circuits 52 and 53, level shift circuits 54 and55, MOS drive circuits 56, 57, 58, and 59, PMOS transistors 60 and 62,and NMOS transistors 61 and 63.

In the driver circuit 12, a switching signal (VIN) from the dataprocessing unit 11 is input to the input circuit 51 in response to thepresence and absence of the foreign matter having a large diameter whichis detected via the sensor 9 and the detection circuit 10, and ON/OFFcontrol of the PMOS transistors 60 and 62 and the NMOS transistors 61and 63 is performed from the input circuit 51 via the level shiftcircuits 54 and 55, and the MOS drive circuits 56, 57, 58, and 59.Further, voltages of VH and VL are generated in the high-voltagegenerating circuits 52 and 53 in response to voltage control signals (VPand VN) from the data processing unit 11. Here, VP represents thevoltage control signal for generating the voltage of VH in thehigh-voltage generating circuit 52, and VN represents the voltagecontrol signal for generating the voltage of VL in the high-voltagegenerating circuit 53. In addition, VH represents a voltage which is ahigh potential and VL represents a voltage which is a low potential froma relationship between potentials which are applied to the PMOStransistors 60 and 62 and the NMOS transistors 61 and 63.

FIG. 3 shows an example of an operation of the driver circuit 12. VIN asa switching signal is a binary signal having low and high potentials andthe respective states are represented by L and H. When VIN is L, thePMOS transistor 60 turns ON from the input circuit 51 via the levelshift circuit 54 and the MOS drive circuit 56, the NMOS transistor 61turns OFF via the MOS drive circuit 57, and VOUTP is the same potentialas VH.

Simultaneously, the PMOS transistor 62 turns OFF via the level shiftcircuit 55 and the MOS drive circuit 58, the NMOS transistor 63 turns ONvia the MOS drive circuit 59, and VOUTN is the same potential as VL. Asa result, a potential difference of VH−VL is applied to the opticalmodulation element 3.

On the other hand, when VIN is H, the PMOS transistor 60 turns OFF, theNMOS transistor 61 turns ON, and VOUTP is the same potential as VL. ThePMOS transistor 62 turns ON, the NMOS transistor 63 turns OFF, and VOUTNis the same potential as VH. A potential difference of VL−VH is appliedto the optical modulation element 3.

Based on the voltage control signals (VP and VN) from the dataprocessing unit 11, generation of VH=V1 and VL=V3, or VH=V2 and VL=V4 isperformed in the high-voltage generating circuits 52 and 53,respectively, and a voltage having switching amplitude: |VH−VL| andoffset voltage: (VH+VL)/2 is applied to the optical modulation element3.

Based on the detection results from the beam power detecting means 13,the switching amplitude and the offset voltage which are applied to theoptical modulation element 3 via the voltage control signals (VP and VN)from the data processing unit 11 are adjusted, and therebycharacteristic fluctuation of the optical modulation element 3 iscorrected such that it is possible to reduce long-term laser powerfluctuation with which the irradiation is performed on the wafer 1.

According to the configuration of the example, the laser power withwhich irradiation is performed on the wafer during inspection isswitched and the long-term irradiation laser power is stabilized. Inthis manner, it is possible to detect the minute foreign matter withaccuracy. Such effects are the same as those to be achieved in theexample which will be described below.

Example 2

FIG. 4 is a diagram of a configuration showing a second embodiment ofthe driver circuit according to the present invention. In order to avoidcomplicated description, the same reference signs are assigned to thesame components as those in Example 1, and thus the descriptions of thecomponents are omitted.

The driver circuit 12 shown in FIG. 4 is configured to include the inputcircuit 51, high-voltage generating circuits 64 and 65, the level shiftcircuits 54 and 55, the MOS drive circuits 56, 57, 58, and 59, the PMOStransistors 60 and 62, and the NMOS transistors 61 and 63. Thehigh-voltage generating circuit 64 generates a voltage in response tothe voltage control signal (VP) from the data processing unit 11, andthe voltage is shifted with VL generated in the high-voltage generatingcircuit 65 as a reference voltage. A potential difference generated inthe high-voltage generating circuit 64 has the switching amplitude:|VH−VL| with respect to the optical modulation element 3. In theembodiment, the potential difference applied to the optical modulationelement 3 is controlled by only the voltage control signal VP, and theoffset voltage to the optical modulation element 3 is controlled by onlythe voltage control signal VN. In this manner, it is possible to changeonly one of the potential difference or the offset voltage, and acontrol method of the optical modulation element 3 by the dataprocessing unit 11 is simplified.

Example 3

FIG. 5 is a diagram of a configuration showing a third embodiment of thedriver circuit according to the present invention. In order to avoidcomplicated description, the same reference signs are assigned to thesame components as those in Example 1, and thus the descriptions of thecomponents are omitted.

The driver circuit 12 shown in FIG. 5 is configured to include aplurality of driver circuits 12 a and 12 b. Respective configurations ofthe driver circuits 12 a and 12 b are the same configurations as thecomponents described in Example 1. Control signals VIN and EN1 are inputto the input circuit 51 of the driver circuit 12 a from the dataprocessing unit 11, and VP1 and VN1 are input to high-voltage generatingcircuits 52 a and 53 b.

In the driver circuit 12 a, predetermined voltages VH1 and VL1 aregenerated by the high-voltage generating circuits 52 a and 53 b, andcontrol of whether or not VOUTP1 and VOUTN1 are output from EN1 isperformed. In a case where EN1 can be output, VOUTP1 and VOUTN1 selectand output VH1 and VL1 in response to VIN1.

Similarly, in the driver circuit 12 b, output permission of VOUTPn orVOUTNn and a selection output of VHn or VLn are performed in response tothe control signals VIN or ENn and VPn or VNn from the data processingunit 11. VOUTP1 and VOUTPn from the driver circuits 12 a and 12 b areconnected to one input of the optical modulation element 3, and VOUTN1and VOUTNn are connected to the other input thereof.

By the driver circuit 12 shown in FIG. 5, the driver circuit can selectan arbitrary voltage set in advance under the control from the dataprocessing unit 11 and can apply the voltage to the optical modulationelement 3. In general, through switching of the voltages by the MOStransistors 60 a to 63 b rather than variable control of the voltages bythe high-voltage generating circuits 52 a, 53 a, 52 b, and 53 b, it ispossible to rapidly switch and control the applied voltage to theoptical modulation element 3, and thus it is possible to perform theirradiation laser power control at a plurality of levels during a periodof wafer inspection.

Example 4

FIG. 6 is a diagram of a configuration showing a fourth embodiment ofthe foreign matter inspection device according to the present invention.Similar to the above description, in order to avoid complicateddescription, the same reference signs are assigned to the samecomponents as those in Example 1, and thus the descriptions of thecomponents are omitted.

In the foreign matter inspection device 100 shown in FIG. 6, predictionof the presence and absence of the foreign matter having a largediameter is performed in the data processing unit 11, and voltageswitching in the driver circuit 12 is controlled. By the predeterminedvoltage switched by the driver circuit 12, the rotation of thepolarization plane of the laser beam passing through the opticalmodulation element 3 is controlled and the laser power of a laser beampassing through the polarization plate 4 is controlled. In addition, inthe data processing unit 11, the beam power detecting means 13 detectsthe laser power with which the irradiation is performed on the wafer 1via the beam splitter 5, and the laser power which is output withrespect to the laser beam source 2 is controlled, based on the detectionresults.

In a case where the polarization plane of the laser beam is rotated andcontrolled by using only the optical modulation element 3 and thepolarization plate 4, a linear relationship is not formed between arotating angle of the polarization plane and the laser power. Therefore,in order to obtain the intended laser power with high accuracy, it isnecessary to control the voltage that is applied to the opticalmodulation element 3 from the driver circuit 12 with high accuracy bythe polarization plane of the laser beam, and the costs of the deviceincrease.

In contrast, by combining the laser beam source 2 as described in theembodiment, there is no need to install high-cost and high-accuracyvoltage generating/controlling means in the driver circuit 12, and thusit is possible to control the laser power with which the irradiation isperformed on the performance wafer 1 with high accuracy.

A configuration in which the MOS transistor is used as voltage switchingmeans is described above; however, another semiconductor switchingelement, a relay, or the like may be used. It is needless to say that itis possible to realize switching of the laser power with which theirradiation is performed on the wafer during the inspection andstabilization of the long-term irradiation laser power under switchingcontrol with respect to the elements and dynamic control of a powersupply voltage which is a connection source.

In addition, switching of the voltages of two values as VH and VL isdescribed above; however, as described in Example 3, it is needless tosay that it is possible to realize the control of the irradiation laserpower at a plurality of levels by switching the plurality of voltageswith driver circuits arranged.

The present invention is not limited to the examples described above,and includes various modification examples.

For example, the examples are described in detail for easy understandingof the present invention, and the present invention is not necessarilylimited to inclusion of the entire configurations described above. Inaddition, it is possible to replace apart of a configuration of anexample with a configuration of another example, and it is possible toadd a configuration of an example to a configuration of another example.In addition, it is possible to add another configuration to, to remove,or to replace, with another configuration, a part of each of theconfigurations of the examples. Specific modification examples are asfollows.

As Modification Example 1, there is provided a flaw inspection devicethat irradiates a specimen surface with a laser beam for a predeterminedtime and inspects a flaw on the specimen surface. The flaw inspectiondevice includes: a laser beam source that emits a laser beam with whichthe specimen surface is irradiated; a modulation unit that modulates theemitted laser beam; a controller that controls a voltage which isapplied to the modulation unit; and a reflected light detecting unitthat detects scattered light reflected from the specimen surface andgenerates a detection signal. The controller performs control to switchthe voltage that is applied to the modulation unit, based on a detectionresult obtained by the reflected light detecting unit.

As Modification Example 2, there is provided a flaw inspection devicethat irradiates a specimen surface with a laser beam for a predeterminedtime and inspects a flaw on the specimen surface. The flaw inspectiondevice includes: a laser beam source that emits a laser beam with whichthe specimen surface is irradiated; a modulation unit that modulates theemitted laser beam; a controller that controls a voltage which isapplied to the modulation unit; and a laser power detecting unit thatdetects laser power which is modulated and with which the irradiation isperformed on the specimen surface. The controller controls the voltagethat is applied to the modulation unit in a case where laser powerobtained at first time and power obtained at second time are differentfrom each other as a result of the detection by the laser powerdetecting unit at the first time and the second time.

As Modification Example 3, there is provided a flaw inspection devicedescribed in Modification Examples 1, the flaw inspection deviceincluding: a laser power detecting unit that detects the laser powerwhich is modulated and with which the irradiation is performed on thespecimen surface. The controller controls the voltage that is applied tothe modulation unit in a case where the laser power obtained at firsttime and the power obtained at second time are different from each otheras a result of the detection by the laser power detecting unit at thefirst time and the second time.

As Modification Example 4, there is provided a flaw inspection devicedescribed in Modification Example 2 or 3, in which the controllerincludes a first voltage generating unit that generates a first voltagewhich is applied to the modulation unit, based on a result detected bythe laser power detecting unit, a second voltage generating unit thatgenerates a second voltage, and a voltage switching unit that switchesthe generated first voltage or the generated second voltage and appliesthe voltage to the modulation unit. The controller performs variablecontrol of the voltages that are generated by the first voltagegenerating unit and the second voltage generating unit.

As Modification Example 5, there is provided a flaw inspection devicedescribed in any one of Modification Examples 1 to 3, in which thecontroller has the first voltage generating unit and the second voltagegenerating unit and applies, to the modulation means, a potentialdifference between the first voltage generating unit and the secondvoltage generating unit.

As Modification Example 6, there is provided a flaw inspection devicedescribed in any one of Modification Examples 1 to 3, the flawinspection device further including the plurality of the controllers.

As Modification Example 7, there is provided a flaw inspection devicedescribed in any one of Modification Example 2 or 3, in which thecontroller controls the laser power of a laser beam that is emitted fromthe laser beam source, based on a detection result obtained by the laserpower detecting unit.

As Modification Example 8, there is provided a flaw inspection method inwhich a specimen surface is irradiated with a laser beam for apredetermined time and a flaw is inspected on the specimen surface. Theflaw inspection method includes: a laser beam emitting step of emittinga laser beam with which the specimen surface is irradiated; a modulatingstep of applying a voltage and modulating the emitted laser beam; acontrol step of controlling the voltage that is applied in themodulating step; and a reflected light detecting step of detectingscattered light reflected from the specimen surface and generating adetection signal. In the control step, the voltage that is applied inthe modulating step is switched, based on a detection result obtained inthe reflected light detecting step.

As Modification Example 9, there is provided a flaw inspection methoddescribed in Modification Example 8, the flaw inspection method furtherincluding: a laser power detecting step of detecting the laser powerwhich is modulated and with which the irradiation is performed on thespecimen surface. In the control step, the voltage that is applied inthe modulating step is controlled in a case where the laser powerobtained at first time and the power obtained at second time aredifferent from each other as a result of the detection in the laserpower detecting step at the first time and the second time.

As Modification Example 10, there is provided a flaw inspection methoddescribed in Modification Example 9, in which the control step includesa first voltage generating step of generating a first voltage which isapplied to the modulating step, based on a result detected in the laserpower detecting step, a second voltage generating step of generating asecond voltage, and a voltage switching step of switching the generatedfirst voltage or the generated second voltage and applying the voltagein the modulating step. In the control step, it is possible to performvariable control of the voltages that are generated in the first voltagegenerating step and the second voltage generating step.

As Modification Example 11, there is provided a flaw inspection methoddescribed in Modification Example 8 or 9, in which the control means hasthe first voltage generating step and the second voltage generating stepand applies a potential difference between potentials obtained in thefirst voltage generating step and the second voltage generating step.

As Modification Example 12, there is provided a flaw inspection methoddescribed in Modification Example 9, in the control step, the laserpower of a laser beam that is emitted in the laser emitting step iscontrolled, based on a detection result obtained in the laser powerdetecting step.

In addition, control wires or information wires are illustrated when thewires are considered to be necessary for description, and all of thecontrol wires or the information wires are not necessarily illustratedfor a product. Actually, almost all of the configurations may beconsidered to be connected to each other.

Example 5

Hereinafter, as Example 5, an example in which a semiconductorinspection device using an optical inspection device is described;however, the example is only an example of the present invention, andthe present invention is not limited to an embodiment which will bedescribed below. In the present invention, the optical inspection deviceincludes a wide range of devices using a laser beam. Hereinafter,examples of the optical inspection device include a system to which theoptical inspection device is connected via a network and a combineddevice of a charged particle beam device, and the devices arecollectively referred to as an optical inspection system.

In the example, examples of the “specimen” include a semiconductor waferhaving a fine pattern, a wafer before the pattern is formed, a photomask(exposure mask), a liquid crystal substrate, or the like.

FIG. 7 is a diagram illustrating a schematic configuration of an opticalinspection device 1 as an example of the semiconductor inspection deviceto which the present invention is applied. An optical inspection device7000 is configured to include a transport system, a stage system, anoptical system, and a data processing system, and the systems arecontrolled by an overall controller 100.

A specimen 7002 is carried to a stage in an inspection chamber by atransport unit 701 that includes a robotic arm therein and is adjacentto the inspection chamber and the specimen is fixed to the stage byvacuum suction or an edge clip.

A specimen stage is configured to have a rotary stage 702, a verticalaxis stage 703, and a horizontal axis stage 704, and a stage controlunit 705 controls the stages. The vertical axis stage 703 causes focussurfaces of an illumination optical system 706 and a detection unit 707to be coincident with the specimen surface, by using a distance sensor(not illustrated) fixed to a reference surface of the illuminationoptical system 706. The stage is moved in a radial direction while beingrotated, and thereby it is possible to inspect the entire surface of thespecimen.

An optical system is configured to include the illumination opticalsystem 706 and the detection unit 707. The illumination optical system706 is configured to include a laser beam source, a lens, and anaperture, and will be described in detail with reference to FIGS. 8 and9. The illumination optical system 706 modulates an illumination beam toan appropriate power, the illumination beam is shaped to have anappropriate spot size, and illuminates the specimen 7002. The detectionunit 707 is configured to include a detector and a detection opticalsystem having a plurality of lenses, concentrates the scattered lightfrom the specimen 7002 on the detector, and converts the detectionresult into an electrical signal to transmit the signal to a signalprocessing unit 709. The optical system control unit 708 controls theillumination optical system 706 and the detection unit 707, andarrangement of optical elements and a gain of the detector are adjusteddepending on inspection conditions.

The signal processing unit 709 appropriately processes a signal inputfrom the detection unit 707 and performs flaw determination. At thistime, a size of a flaw is determined, based on the intensity of thesignal. In addition, a coordinate of the flaw is determined, by using anencoder signal input from the rotary stage 702 and the horizontal axisstage 704.

Data processed in the signal processing unit 709 is transmitted to anoverall controller 700, and is displayed on a display 710 or is storedin a storage unit 711 as a data file.

A configuration of the system is not limited thereto, and a part or theentirety of a device constituting the system may be a common device.

The overall controller 700, the stage control unit 705, the opticalsystem control unit 708, and the signal processing unit 709 can berealized in any type of hardware or software. In a case of aconfiguration as the hardware, the units can be realized by integratinga plurality of computing elements that execute processes on a wiringboard, or in a semiconductor chip or a package. In a case of aconfiguration as the software, the units can be realized by causing acentral processing unit (CPU) mounted on the device constituting thesystem or a general-purpose CPU mounted on a general-purpose computerconnected to the system to execute a program for executing a desiredarithmetic processing.

FIG. 8 shows an example of a configuration of the illumination opticalsystem 706. The illumination optical system is configured to include alight source 800, a power control unit 801, and a beam shaping unit 802.

For example, a laser beam source is used as the light source 800. Inorder to detect a minute flaw in the vicinity of the specimen surface,an ultraviolet or vacuum ultraviolet laser beam having a shortwavelength is oscillated and a high power light source having a power of1 W or higher is used.

The beam shaping unit 802 is an optical unit that forms a predeterminedillumination shape and is configured to include a beam expander, forexample.

The power control unit 801 is mainly configured to include a Pockelscell 804, a half-wave plate 805, a polarization beam splitter 806, andan attenuator (static attenuator) 807. Hereinafter, an example in whichthe Pockels cell is used as an example of the electro-optic element willbe described; however, an element of which a polarization direction ofbeam is electrically switched may be used. The laser beam incident onthe Pockels cell 804 is subjected to phase modulation depending on anapplied voltage from a Pockels cell control unit 808. Further, a certainamount of the laser beam is subjected to the phase modulation by thehalf-wave plate 805 disposed at the back of the Pockels cell and isincident on the polarization beam splitter 806. Here, it is importantthat the half-wave plate 805 is in front of the polarization beamsplitter. The half-wave plate 805 is fixed to the rotary stage 818 andcan be placed at any angle. A half-wave plate control unit 809 controlsa placement angle. The placement angle used in the example is two typesof 0° and 45° and, in order to obtain a phase modulation effect of thetwo types of placement angles, the 45°-placed half-wave plate may beconfigured to be loaded and unloaded on an optical path by a directlymoving stage.

The beam subjected to the phase modulation by the Pockels cell 804 andthe half-wave plate 805 diverges into two optical paths by thepolarization beam splitter 806. The beam transmitted through thepolarization beam splitter 806 is referred to as the inspection beam andthe reflected beam is referred to as non-inspection beam. It is possibleto adjust a ratio of the inspection beam and the non-inspection beam bythe Pockels cell applied voltage and the placement angle of thehalf-wave plate.

The non-inspection beam is transmitted through a beam sampler 810 and isincident on a diffuser 811. Here, an element having an amount of thereflected beam which is larger than an amount of the transmission beamis used as the beam sampler 810. A part of beam reflected from the beamsampler 810 is caused to be incident on a power monitor 812 and a powerlevel is always monitored.

A power monitor signal is input to the Pockels cell control unit 808 andis used to detect abnormality of the Pockels cell, and to optimize thePockels cell applied voltage.

In a case where a control signal and the power monitor signal arecompared to each other in the Pockels cell control unit 808 and a powerthat is not coincident with the control signal is detected, an interlockcircuit that closes an optical path shutter 813 is used.

The optical path shutter 813 is disposed at the back of the polarizationbeam splitter 806 that forms divergence to the power monitor 812, andthereby it is possible to check that correct control is performed beforethe specimen 7002 is illumined.

Further, the maximum value of the illumination power is limited by theattenuator 807 at the final end of the power control unit, and it ispossible to limit the irradiation power to the specimen and a fail-safeis realized even in a case where it is not possible to control theintensity modulation by the Pockels cell.

Since the Pockels cell 804 has characteristics that change depending onthe temperature, a thermometer 815 and a heater 816 are provided in thepower control unit 201, and a temperature control unit 817 controls thetemperature to be a constant temperature. A cooler may be used insteadof the heater 816, or a unit having a function of performing both of theheating and cooling may be used.

As described above, it is possible to take measures of constanttemperature control with respect to a relatively long-term temperaturefluctuation, and it is effective to improve reliability of theperformance of the inspection device.

FIG. 9 shows another example of a configuration of the illuminationoptical system 706. The configuration differs from that in FIG. 8 inthat a beam sampler 910 is disposed on the optical path of theinspection beam and a part of the inspection beam is monitored by thepower monitor 812. Here, an element having an amount of the reflectedbeam which is larger than an amount of the transmission beam is used asthe beam splitter 910. In this case, the optical path shutter 813 isdisposed at the back of the beam sampler 810. According to theconfiguration in FIG. 9, unlike the configuration in FIG. 8, since theinspection beam itself diverges and is monitored, it is possible to moredirectly check the state of the inspection beam.

Next, the power modulation using the Pockels cell is described withreference to the figures.

FIG. 10 shows a relationship (intensity modulation characteristics)between the Pockels cell applied voltage and the inspection power. Whena voltage is applied to the Pockels cell, a polarization axis is rotatedwith respect to a transmission axis of the polarization beam splitter806, and thus voltage characteristics (intensity modulationcharacteristics) 1000 as shown in FIG. 10 are obtained. When a voltageVLmin1001 is applied, the polarization axis is rotated by 90° withrespect to the transmission axis of the polarization beam splitter 806and the minimum inspection beam power is obtained. When a voltageVHmax1002 is applied, the polarization axis is coincident with thetransmission axis of the polarization beam splitter 806 and the maximuminspection beam power is obtained. A voltage obtained when thepolarization axis is rotated by 180° is referred to as a half-wavevoltage VHW1003 and is an index of the voltage characteristics of thePockels cell.

FIG. 11(a) shows an example of the Pockels cell applied voltage. ThePockels cell applied voltage has a first level VL1101 and a second levelVH1102 as references. The Pockels cell control unit can arbitrarilydesignate the levels. For example, when the first level is set to thevoltage VLmin at which the minimum inspection power is obtained, and thesecond level is set to the voltage VHmax at which the maximum inspectionbeam power is obtained, the applied voltage is switched to VLmin andVHmax, and thereby it is possible to switch between the minimum powerand the maximum power. A ratio of the minimum power and the maximumpower is determined by an extinction ratio of the Pockels cell and, ingeneral, 1:50 to 1:1000. In a case where the Pockels cell having theextinction ratio of 1:50 is used, it is possible to perform switching toa power of 2% of the maximum power when the maximum power is 100%.

In addition, when a plurality of levels are set between VLmin and VHmaxas shown in FIG. 11(b), it is possible to obtain any power between 2% to100%.

For example, in a case where large foreign matter is present on thespecimen surface and a position thereof is found in advance using anymethods, switching to a control voltage is performed in the vicinity ofthe large foreign matter and the inspection power is reduced. Hence,while the explosive fracture of the large foreign matter is suppressed,it is possible to increase the inspection power in the other region andto inspect the region with high sensitivity. Examples of a method offinding the large foreign matter in advance are considered to include amethod of performing pre-inspection before the main inspection, aprevious detection method using an end portion of the inspection lightbeam, or the like.

The phase modulation effects of the Pockels cell are changed due to notonly the applied voltage, but also the temperature. FIG. 12 shows anexample in which the voltage characteristics of the Pockels cell arechanged due to the temperature. The voltage characteristics 1200 at acertain reference temperature (T=T0) are changed to 1201 due to atemperature drop (T=T1) and are changed to 1202 due to a temperaturerise (T=T2). In other words, the voltage, by which the maximum power ofthe inspection beam is obtained, is changed. It is necessary to controlthe temperature around the Peckels cell such that the temperature isconstant; however, the temperature control is performed with lowaccuracy and a reaction rate is also delayed. Hence, it is preferablethat correction of the influence of a relatively short-term temperaturefluctuation is performed by the applied voltage.

FIG. 13 is a flowchart illustrating voltage correction flow. In order tofirst prevent erroneous irradiation before an inspection start, anoptical path shutter 813 is closed (Step 1301). In order to acquirevoltage characteristics as shown in FIG. 10, the applied voltage to thePockels cell is changed in a certain range and pitch such that data ofnon-inspection beam power is acquired, and the data is stored in theintensity modulation characteristic storage unit 814 in FIGS. 8 and 9(an intensity modulation characteristic storing process in Step 1302).VLmin is obtained from the acquired voltage characteristic data (Step1305). In a case where whether the value of the obtained VLmin satisfiesconditional Expression 1304 is checked and the value does not satisfythe expression, the placement angle of the half-wave plate is changed (awave plate angle adjusting process in Step 1305). Here, ConditionalExpression 1304 represents a condition for suppressing the inspectionbeam power obtained in a state in which the applied voltage is 0 to beequal to or lower than 50% of the maximum power obtained in a state inwhich the voltage is applied (FIG. 8 showing a reason why it is possibleto suppress the power to be equal to or lower than 50%). When VLmin thatsatisfies Conditional Expression 1304 is determined, and VHmax iscalculated from VLmin and is registered as a constant representing thevoltage characteristics of the Pockels cell (Step 1306). Here, acalculation expression depends on FIG. 10. VL and VH that are actuallyused as the control voltage are obtained from VLmin and VHmax and areregistered (Step 1307). Here, fixed values 1 and 2 used when VL and VHare obtained are constants that are determined, depending on levels ofthe maximum power and the minimum power.

Finally, VL is set as the voltage value obtained at the time ofinspection start (Step 1308). After a stable state is set, the shutteris opened (Step 1309) and the inspection is started.

In other words, the voltage correction flow shown in FIG. 13,particularly, the intensity modulation characteristic storing process(Step 1302) is always executed before the inspection, and thereby it ispossible to repeat and store the influence of the relatively short-termtemperature fluctuation as a type of fluctuation of the voltagecharacteristics of the Pockels cell. Therefore, the voltage is appliedto the Pockels cell at the time of the inspection, based on the storedintensity modulation characteristics, and it is possible to correct theinfluence of the temperature fluctuation.

Here, an expression, during the inspection, means that it is the time inthe middle of execution of the inspection on the specimen 7002 which isperformed by illuminating the laser beam of the illumination opticalsystem 706 on the specimen 7002, receiving the scattered light from thespecimen 7002 by the detection unit 707, and then performing the flawdetermination in the signal processing unit 709. In addition, anexpression, before the inspection, means that it is the time before theinspection is performed, that is, it is the time including not onlyimmediately after the specimen 7002 is transported into the inspectionchamber, but also before the next predetermined inspection is performedafter a predetermined inspection is ended.

A table in FIG. 14 is to show that it is possible to suppress theinspection power obtained in a case where the applied voltage is 0 to beequal to or lower than 50% of the maximum power obtained in a state inwhich the voltage is normally applied by the rotary wave plate (a waveplate angle adjusting process). The horizontal axis represents a valueobtained by normalizing the applied voltage into a half-wave voltage,and the vertical axis represents the inspection beam power. A state 1and a state 2 represent different temperature states from each other.

In the state 1, in a case (1400) where the half-wave plate placementangle is 0°, the transmission power is lower than 50% even when it isnot possible to apply the voltage during the inspection (that is, V=0).However, in the state 2, in a case 1401 where the half-wave plateplacement angle is 0°, the transmission power is higher than 50% at themoment when the application of voltage is stopped. In a case of thestate of 1401 in which the optimization is performed before theinspection, Conditional Expression 1304 in FIG. 13 is not satisfied, andthus the half-wave plate is rotated. Then, since the state of 1401 isswitched to a state of 1403, the inspection power is lower than 50% in astate in which it is not possible to perform the voltage control.Similarly, since a state of 1402 does not satisfy Conditional Expression1304, the half-wave plate is rotated and the state is switched to thestate of 1400. In other words, the half-wave plate is placed at 0° suchthat the characteristics as in 1400 are obtained when the temperature isin the state 1, and the half-wave plate is placed at 45° such that thecharacteristics as in 1403 are obtained when the temperature is in thestate 2. In other words, an offset is applied to a phase on the waveplate such that the power of the minimum inspection beam (preferably, 0)is obtained when the applied voltage to the Pockels cell is 0.

According to the example, even in a case where any type of abnormalityoccurs in the Pockels cell itself or the Pockels cell control unit, andthe voltage is not applied, it is possible to limit the transmissionpower to be equal to or lower than 50% of the maximum power in a statein which the voltage is applied. In this manner, it is possible tominimize a risk of damaging the specimen 7002.

In addition to this, it is possible to correct the influence of therelatively short-term temperature fluctuation to the extent that thetemperature changes for each time of the inspection by the voltagecharacteristic data acquisition/storage 1302 (intensity modulationcharacteristic storing process) before the inspection shown in FIG. 13or the registering 1306 of VLmin and VHmax in response to theacquisition and storage, and thereby it is possible to not only suppressthe explosive fracture of the large foreign matter with high accuracy,but also to obtain the maximum inspection beam power during normalinspection with high accuracy. Hence, it is possible to realize theimprovement in the inspection sensitivity.

The present invention is not limited to the examples described above,and includes various modification examples. For example, the examplesare described in detail for easy understanding of the present invention,and the present invention is not necessarily limited to inclusion of theentire configurations described above.

In addition, control wires or information wires are illustrated when thewires are considered to be necessary for description, and all of thecontrol wires or the information wires are not necessarily illustratedfor a product. Actually, almost all of the configurations may beconsidered to be connected to each other.

REFERENCE SIGNS LIST

1: wafer

2: laser beam source

3: optical modulation element

4: polarization plate

5: beam splitter

6: mirror

7, 8: lens

9: sensor

10: detection circuit

11: data processing unit

12: driver circuit

13: beam power detecting means

14: stage

51: input circuit

52, 53: high-voltage generating circuit

54, 55: level shift circuit

56, 57, 58, 59: MOS drive circuit

60, 62: PMOS transistor

61, 63: NMOS transistor

64, 65: high-voltage generating circuit

100, 110: foreign matter inspection device

7000: semiconductor inspection device (optical inspection device)

7002: specimen

706: illumination optical system

800: light source

804: Pockels cell

805: half-wave plate (wave plate)

806: polarization beam splitter

807: static attenuator

808: Pockels cell control unit

809: half-wave plate control unit

812: power monitor

814: intensity modulation characteristic storage unit

1000: intensity modulation characteristics

1302: intensity modulation characteristic storing process

1305: wave plate angle adjusting process

The invention claimed is:
 1. A semiconductor inspecting devicecomprising: an illumination optical system that includes a laser beamsource; an electro-optic element on which a laser beam from the laserbeam source is incident; a polarization beam splitter on which the laserbeam transmitted through the electro-optic element is incident; and ashutter that is provided on an optical path of the laser beamtransmitted through the polarization beam splitter, wherein, when theshutter is closed intensity modulation characteristics of theillumination optical system are acquired with respect to a voltageapplied to the electro-optic element, and wherein the illuminationoptical system is corrected based on the acquired intensity modulationcharacteristics, such that an illumination beam having a first intensityand an illumination beam having a second intensity that is higher thanthe first intensity are outputted from the illumination optical system,and an inspection of a specimen is performed in a state in which theshutter is opened.
 2. The semiconductor inspecting device according toclaim 1, wherein, during the correction, a phase fluctuation of theelectro-optic element itself is corrected, based on the acquiredintensity modulation characteristics.
 3. The semiconductor inspectingdevice according to claim 1, wherein, during the correction, anintensity of the laser beam from the laser beam source is adjusted.
 4. Asemiconductor inspecting device comprising: a stage for mounting aspecimen; a detection unit; and an illumination optical systemcomprising a laser beam source; a polarization beam splitter; anelectro-optic element on an optical path between the laser beam sourceand the polarization beam splitter; and a shutter which can be openedand closed, wherein, when the shutter is closed, intensity modulationcharacteristics of the illumination optical system are acquired withrespect to a voltage applied to the electro-optic element, wherein, whenthe shutter is closed, the illumination optical system is correctedbased on the acquired intensity modulation characteristics, such thatthe illumination optical system is able to output an illumination beamhaving a first intensity and an illumination beam having a secondintensity that is higher than the first intensity, and wherein, when theshutter is opened, an inspection of the specimen is performed.
 5. Thesemiconductor inspecting device according to claim 4, wherein, duringsaid correction of the illumination optical system, a phase fluctuationof the electro-optic element itself is corrected, based on the acquiredintensity modulation characteristics.
 6. The semiconductor inspectingdevice according to claim 4, wherein, during said correction of theillumination optical system, an intensity of a laser beam from the laserbeam source is adjusted.
 7. The semiconductor inspecting deviceaccording to claim 4, wherein, when the shutter is closed, the shutterblocks a laser beam from the laser beam source through the polarizationbeam splitter.